Process for solvent extraction of oil



Patented Dec. 9, 1941 UNITED STATES] PATENT oFFiee David' R. Merrill, Lon Beach, Calif., ,as'sigfi6fjto Union Oil Company of Galifor'nia, L65 Ang'eles'; Calif., 21; corporationof California;

Application Jan-uary' 19, 1934', SeriaiNo; 707,32

15" Claims; 01. mea -43) This invention relates to-the extraction of oils by employing a selective solvent. Although applicable to the treatment of other oils; it refersmore particularly to the production of lubricating, oil-by a selective solvent extraction process;

It has been found that desirable paraffinic hydrocarbons can be separated from the undesirable olefinic. naphthenio and/or aromatic compounds by the use of solvents which selectively dissolve the undesirable hydrocarbons but which exhibit only a very limited solvent pow-erupon the desirable parafiinic hydrocarbons;

When I use the term parafilnichydrocarbons I mean those highly saturated compoundswhich are present inpetroleum and are characterized by low temperature viscosity susceptibility, i. ethey exhibit a minimum change inviscosity fora given change in temperature. They also are characterized by relative stability toair and sunlight, exhibiting little tendency toward discoloration or sludgeformation. This definition is notvmeant to include those compounds which are usually solid or semi-solid at ordinary temper-- aturesand which are known as wax or petrolatum, but, of course, it is obvious that my invention is meant to also include the selective' extraction of waxy oils; As a: matter of convenience hereafter, I will refer to the undesirable components, such as-o1efinic,.naphthenic and/oraromatic hydrocarbons, as the non-parafiinic components of petroleum. These fractions are characterized by a relatively high temperature viscosity susceptibility and are relatively unstable to air andsunlight exhibiting discoloration and sludge formation.

A number of selective solvents for extraction have been found, fol-example, it has. been shownthat such materials as aniline; chloraniline, nitrobenzene, dichlorethyl' ether,. phenol,v chloro-* phenol,.cresol and cresol with a small-proportion of water, for instance 4%, are highly selective as solvents for the non-paraflinic hydrocarbons. When these. solvents are commingled with petroleum or petroleum fractions under the: proper conditions of temperature; the undesirable non-- parafiinic hydrocarbons pass into solution to a:

greater or less extent but a substantial proportion of the desirable parafiinic hydrocarbons-remainsundissolved. The solution of undesirablehydro carbons and solvent settles to the bottom of the:

container and forms an extract phase when rel-- atively heavy solvents are employed- The relatively light: par'afiinic hydrocarbons rise to the top of the vessel and: form a rafiinate phase.

These phases are then: readily separablerby" or ess.

dinary decantation means; The rafiinate phaseis: usually found tocontain a small quantity of. the selective solvent and the extract phase or.- din'arily" contains a relatively large quantity of the solvent. These fractions may be purified by distillation whereby the solvent isdistilledaway from the hydrocarbon oils. I I

I have found that in the usual'solvent: extrac: tionof mineral oil: with the above mentioned selectivesolvents, the separation is. not complete.- Particularly, all of: the para-ffinic hydrocarbons: i. e. the more valuable lubricants, are not; obtained' in thearafiinate phase but=instead some-ofthe oil fractions: which: arepreferred in. the rafli nateare found-in the extract phase? Gonverselysome fractionsdesired in the" extract phase are; found associated with the ra-flinate aster usualextraction. I I

It hasbeen known inthesolvent extraction art that after making. a primary separation 0t raffinate from extract, additional fractions can be made to separate from the extract phase by one or more reductions of temperature w-hich ochrespondingly reduce the solubility of theseoils of relatively high paraffinicity in the extract phase.

These oils.- then form intermediate rafiinates Which can be separately recovered by decantation from the remaining extractphase. I I

I have discovered that if a material which; I

term an anti-solvent added toanex-tract'phase.

produced by' extraction with a selective solvent, the extract phase can itself. be separated into afurther extract. and ra-ffinateofi lower and higher quality, respectively than the original extract Also if an' anti-solvent is present duringatlea'st one of the extraction stages, those fractionsdesired in the rafiinatew-ill be forced; into this; phase by: action of this material. without necessarily; refrigerating the oil subjected to err-- traction to the degree heretofore found necessary to'render substantially all of those fractionsde sired the raffinate insoluble in theextract;

phase. In fact; in some cases thereduction of,

temperature may be entirely omitted inmy proc- In a solvent extraction process of thischaracter, the expense of refrigeration is a'substantial item in* the cost of operations My processlowers this cost. I I I I An anti-solvent maybe defined as amaterial which tends to prevent the solution of Y a hydrocarbon fractionwhich, except for the presenceof the' anti-solvent, would be; dissolved inthe ex.- tract' phase upon extraction of the oil with: a selective? solvent; I have: foundthat anumber of substances" are suitable for use as an antimy process.

.butane, or methyl, ethyl or isopropyl alcohols,

methyl cellosolve (mono-methyl ether of ethylene glycol), carbitol (mono ethyl ether of diethylene glycol) and other oxygenated compounds such asacetone or methyl acetate. Even water may be used as an anti-solvent when the selective solvent with which it is employed is at least partly soluble therein. One or more of these anti-solvents may be employed.

Extraction of the oil may be accomplished by a.v selective solvent modified or unmodified, as de- J.

sired, by the presence of an anti-solvent and to, the extract phase thus produced is .added,sufii-; cient anti-solvent to cause phase separation of My invention also includes V this extract phase.

primarily extracting an oil with a selective solvent to produce a raffinate phase and an extract;

phase and further extracting this extract phase with a selective solvent in the presence of an anti-solvent. If-desired, the primary extraction can be'in' the presence of an anti-solvent and the extraction of the extract phase can be with a' selective" solvent to which further quantities of anti-'solventare added.

I havealso found that in the usual selective solvent 'e'xtraction of mineral oil, some of the' fractions desired in the extract phase are foundv associated with the rafiinate. In order to obtain a high quality raiiinate, it is necessary that these fractions be removed. I have discovered that this maybe accomplished by extracting the oil in stages-in-which thesolvent power of the selective solvent employed is increased in each successive stage' A-final raflinate is thereby obtained which is substantially free of fractions de- 1 sired in the extract phase. This may be accomplished by first extracting the oil with a selective i solvent in the" presence of a relatively large. amount of anti-solvent and then extracting the raflinate from this extraction with a selective solvent associated with less or no anti-solvent.

- It is'an object of my invention to extract oil with asolven't'in the presence of an anti-solvent to force into the rafiinate phase that portion desired. the raffinate which would otherwise remainin the extract phase; 7

It is a further object to extract an oil with a selective solvent, separate the rafinate from the extract thereby obtained and intermix said extract with an anti-solvent to separate an intermediate rafiinate from said extract. 7

It is 'another object of my invention to separation of parafiinic and non-parafiinic hydrocarbons into rafiinate and extract phases, ree spectively.

, A further object of my invention is to produce .ob; tain" the desired material in the raffinate phase; without refrigerating to the temperatures here- Q tofor e found necessary for relatively complete number'of stages of extraction and anti-solvent by extraction with a selective solvent a raflinate substantially free of material desired inthe extract phase. In the drawing: a

Fig. 1 is a schematic arrangement of one form 1 of apparatus which may be employed to'carry out Fig. 2 is another form of appa-' ratuswhich I'may employ.

jl'1.eferring more particularly to Fig. l, extractors" "land I! are provided. Oil to be subjected. to extraction is fed by actionof pump I5 into extractor. I0 through line l3 controlled by'valve l4, Solvent is introduced into extractor ID by. action of pump in line I! controlled by valve I8. Raflinate is removed from extractor I!) through line 20 controlled by valve 2|. Extract phase from H] passes through line 22 controlled by valve 23 into coil 24 in cooler 25. As previously stated, the extraction in the first stage, i. e. in extractor l0 does not separate all of the material desired in the rafiinate. Some of the material preferred in the rafilnate remains dissolved in the extract phase. Accordingly, after the separation in extractor l0 into raffinate and extract phases, it is further necessary to separate an intermediate raflinate from the extract phase passing from coil 24 via line 21.

In order to obtain this intermediate raifinate, an anti-solvent. is passed into line 21 by action of pump 30 from line 3| controlled by valve 29. The

extract phase and anti-solvent are then passed into an agitator such as orifice mixer 32 where these materials are thoroughly contacted. The mixture is then passed into extractor ll through linev 33 and flows countercurrently. to selective solvent entering through line 34 controlled by valve 35 by action of pump 36. Rafiinate phase is removed from H through line 3! controlled by valve 38. Extract phase exits from. H through line controlled by valve 4|.

In view of the foregoing it is obvious that the oil in extractor I0 is separated into an extract and a raffinate. As previously stated, this separation is not complete because some of the fractions associated with the extract are desired. in the rafiinate phase. The selective solvent employed for extraction in In may be unmixed with anti-solvent or in some instancesv this primary extraction may take place in the presence of an anti solvent. In .order to obtain thorough extraction and phase separation in extractor II it is necessary that the temperature prevailing, therein be less than that in extractor I when no,

additionalanti-solvent is. introduced with the solvent entering via line 34. In fact, the temperature in'l I may be lower in! I even when antisolvent is added with 'the selective solvent through line 34 but sufilcient anti-solvent may be introduced therewith so that it does not become necessary to' reduce the temperature in II below that prevailing in ID. Because the solvent power of the solvent is decreased in extractor I i, an intermediate. rafiinate is separated therein from the primary extract. ,The extract passing through line 40 is relatively free of those fractions desired in the rafiinate.

"Int orderto' remove the solvents: and anti-solvents from the extracts and rafiinates associated therewith, these materials maylbe distilled there-.

from in the usual manner. .It is obvious thatin place of-thetwo stage systemzdescribed a greater addition may be provided.

As an example of the operation of the. apparatus disclosed in Fig. 1, petroleum lubricating oil, in extractor 10 was extracted with 150 volume percent.-of phenol at 125 F. The extract phasewas cooled in coil 24 to F. and water was added as an anti-solvent via line 3| in the proportion of volume percent. based on the oil'originally charged to the system. Extraction took place in II by the addition of 50 volume'percent. phenol containing 9% Water via line 34. ltwasfound;

that the'intermediate raffinate flowing through line 31 contained valuable paraffinic fractions.

which would-otherwise have been lost in the ex tract flowing fromextractor. IIJ via line 22.

. Referring more particularly to Fig. 2, continuous, countercurrent extractors I00, and I01 are provided and oil to be subjected to extraction is fed by action of pump I=02 into extractor I through line I03 controlled by valve" I00. Solvent is introduced into extractor IIII by action of pump I05 in line I06 controlled by valve I01. Thefinal extract phase separated from the rafiinate phase is removed from the system bypassing from extractor I00 through line I08 controlled by valve I09. Final rafiinate phase is-removed from extractor I-0I via line IIO controlled by valve I I I An intermediate raifinate fraction can be separated and removed via line I33 in: a manner to-be described. I

The oil entering the system through line I03 is subjected to extraction in extractor I00, preferably by passing countercurrently to and in direct contact with a stream of extracting mediiun to be described entering through line H2. The raffinate from this extraction is removed from I00 through line II3 controlled by valve IM'. It passes through coil H5 disposed in heater H0 and then travels through line I'I'I into extractor I-0I-. Extraction proceeds in I01 by flowing the oilentering via II'I in direct contact with selective solvent entering through line I06.

Intermediate extract phase is removed from extractor I0 I through line I by pump I2I-. As" previously described, some'oil fractions which are desired in the raflinate phase do not remain insoluble in the extract phase and are associated therewith in the stream passing through line I20. Accordingly, afterthe separation in extractor I01 into final raffinate and intermediate extract phases, it is further necessary to separate an intermediate raffinate from the intermediate ex-- tract phase leaving through line I20. By action of pump I2I an anti-sol vent may be introduced into line I20 through line I22 controlled by val-ve I23. The material flowing through line- I20' is then brought to the correct temperature by passage through coil I25 in cooler I26. The material from coil I25 flows via line I20 to an agitator such as orifice mixer I for thorough agitation and. intermixture with the anti-solvent. Fromthis agitator the mixture flows via line I-3 I into intermediate separator I32 wherein phase separation takes place. The intermediate rafiinate phase is removed through line I33 controlled. by valve I34. Extract phase from separator I32 freed from intermediate raffinate is removedtherefrom by action of pump I35 through line II2 controlled by valve I37 and passes into extractor I00. Thus, the extract phase from separator I32- enters extractor I00 and the solvent associated therewith and modified by the anti-solvent is used as the extracting medium for the oil passing to the extractor I00 via line I03. The extract phase in line II2 may be heated or cooled, asnecessary, to obtain the desired phase separation in extractor I00.

Inview of the foregoing it is obvious that the oilentering extractor I00 is separated therein into an extract and a rafrlnate by a selective solvent Whose solvent power is reduced by the presence of an anti-solvent. As previously stated, this separation is not complete because some of the fractions associated with the raffinate are desired in the extract phase. Consequently, the oil leaving extractor I00 through line I I3 is in effect partially extracted oil. The extraction in I00 occurs by direct contact with a mixture of one or more of the above mentioned solvents with one or more of the above mentioned anti-solvents. The partially extracted oil. from I00 is further extracted in HM with solvent preferably unmixed portion of anti-solvent. Due to the. relatively high solventpowerof the selectivesolvent in I 0 I, the raffinat'e separated therefrom contains little orno fractions desired in the extract phase.

The temperature in extractor IOI may bethesame as that prevailing in extractor I00 or the temperature may be increased. In order to free the respective extracts and raflinates from the solvent and anti-solvent associated therewith these materials may be distilled from the extract and raflinatein any usual manner. While I have shown and. described a two stage system, in some cases it may be desired to add more extraction stages than here shown and to employ more steps of. anti-solvent addition. These modifications will. appear obvious to one skilled in the art.

By employing ananti-solvent in: the manner described above, extremely low temperatures in extractor I00 otherwise necessary to prevent an excessive amount of extraction at this point are avoided. By avoiding such low temperatures, the process is better adapted for operation on oils ofv high viscosity or high pour point. The process is also better adapted to operation with solvents of relatively high solidification temperature such as nitrobenzene or phenol.

As an; example of: the operation of the apparratu'si disclosed? in. Fig- 2,. petroleum lubricating oil was extracted withv 1 50- volume percent. of phenol entering via line I 00; As an anti-solvent there was introduced 15 volume percent. based on the oil feed, of water to' the extract phase flowing through. line I20. The temperature in extractors I00 and I-:0 I and separator I32 were F., and 60 F., respectively- It was found that by this treatment that portion of the railinate flowing through line H31Whl'0h was desired in the extract phase could be removed from the ramnate phase before passage through line IIO' from extractor IOI. Furthermore, an additional separation into extract and rafinate phases could be accomplished in the presence of the anti-solvent in separator I32.

The viscosity gravity constant, abbreviated V. G. C., is an index of the paraffinicity or naphthenici-ty of an oil. A high value represents a high degree of naphthenicity while low values indicate relatively greater paraflinicity. This constant is determined by the method employed by Hill and Coates as set forth in the intermediate rafiinate passing via line I33 had-- a V. G. C. of 0.86 and the extract returnedv to extractor I00 through line II2' had a V. G. C. of.

0.92. It is thus evident that after removal of the least valuable, highest V. G. C. fractions in extractor I00, a high quality final raflinate was obtained: from the stock and from the extract phase produced in extractor IOI there was obtained an intermediate raflinate of better quality than the material flowing through line I 20'.

In some cases my process may simply comprise extracting an oil with a selectivesolvent, separating. the extract phase from the raffinate phase,

adding anti-solvent to the extract phase, cooling the latter mixture: if necessary to produce an with ananti-so1ventl or mixed with a smaller. pro

When oil of 0.86.

intermediate raflinate insoluble in the extract phase by virtue of the addition of the antisolvent and separately removing from the ex-.

traction system. the intermediate rafiinate and the extract phase freed of this intermediate raf- The initial rafiinate, intermediate raffinate and extract freed from intermediate raffinate were relatively high, ,medium and low grade oils, respectively. The solvent and anti solvent may be removed from the fractions containing the same by any usual means such as by distillation. As an example of this operation,

petroleum lubricating oil was extracted with 150 volume percent. cresol at 60 F., and the phases were separated. To the extract phase wasadded '7 of my invention.

I claim:

1. A process for the separation of paraflinic and non-paraffinic fractions from mineral oil containing the same which comprises extracting said oil with a selective solvent, separating the extract phase soluble in said solvent from the raflinate phase insoluble therein, commingling said extract phase with an anti-solvent and extracting said mixture of extract phase and antisolvent with a further addition of selective solvent to separate an intermediate rafiinate insoluble in said solvent from the extract phase soluble therein.

2. A' process for the separation of parafiinic and non-paraffinic fractions from mineral oil containing the same which comprises extracting said oil with a selective solvent, separating the extract phase soluble in said solvent from the raflinate phase insoluble therein, commingling said extract phase with an anti-solvent and extracting said mixture of extract phase and anti solvent with a further addition of selective solvent at a temperature lower than the temperature of said first mentioned extraction to separate an intermediate raffinate insoluble in said solvent from the extract phase soluble therein.

3. A process for the .separation of para-fiinic and non-parafiinic fractions from mineral o l containing the same which comprises extracting said oil with a selective solvent, separating the theseparated oil phases.-

4. A process for the separation of paramnic and non-parafiinic fractions from mineral oil containing the same which comprises extracting said oil with a selective solvent,.separating the extract phase soluble in said solvent from the rafiinate phase insoluble therein, extracting 'said' extract phase with a further addition of selective .solvent in the presence of an anti-solvent to sepa-. rate an intermediate rafiinate insoluble in saidv solvent'from the extract phase soluble therein and removing the solvent and anti-solvent from extract phase soluble in. said solvent from the raifinate' phase insoluble therein, commingling',

said extract phase with an anti-solvent to separate an intermediate raflinatefrom said extract phase and extracting oil with selectivesolvent' comprisingsaid extract phase freed from .;said intermediate raffinate. '5.

.5. Aprocess for the separation 'of paraffinic and non-parafiinic fractions from mineral oil containing the same which comprises extracting said oil with a selective solvent, separating the extract phase soluble in said solvent from the rafiinate phase insoluble therein, further extracting said raffinate phase with selective solvent, separating a final raffinate insoluble in said solvent from intermediate extract phase soluble therein, commingling said intermediate extract phase with anti-solvent, separating an intermediate raflinate from said intermediate extract phase and returning as selective solvent to said first mentioned extraction said intermediate extract phase freed from said intermediate raffinate.

6. A process for the separation of parafiinic and non-paraffim'c fractions from mineral oil containing the same which comprises extracting said oil with a selective solvent, separating the extract phase soluble in said solvent from the raffinate phase insoluble therein, further extracting said rafilnate with selective solvent at a higher temperature than the temperature of said first mentioned extraction, separating a final rafi'inate insoluble in said solvent from intermediate extract phase soluble therein, commingling said intermediate extract phase with anti-solvent and cooling the same, separating an intermediate raffinate from said intermediateextract phase and returning as selective solvent to said first mentioned extraction said intermediate extract phase freed from said intermediate raffinite.

7. A method as claimed in claim 4 in which the selective solvent is one of the members selected from the group of aniline, nitrobenzene, dichlorethyl ether, phenol and cresol.

8. A method as claimed in claim 4 in which the selective solvent is phenol and the anti-solvent is water.

9. A method as claimed in claim 2 in which the anti-solvent is an alcohol.

10. A process for the separation of parailinic and non-paraffinic oil fractions from a mineral oil containing the same which comprises come mingling said oil with a selective solvent for the non-paraffinic fractions and an anti-solvent adapted to lower the solubility of the paramnic fractions in the selective solvent which is more soluble in the extract phase than in the raffinate phase and thereby forming a raffinate phase and an extract phase, separating said phases, 7. re-

extracting the rafiinate with a selective solvent and thereby forming a second raifinate phase and a second extract phase and separating said sec ond formed phases. Y

11. A process for the separation of mineraloil. into fractions relatively more paraffinic in char-.

acter and relatively less parafiinic in character than the original oil which comprises extracting said oil in a plurality of stages with a selective solvent for non-paraffinic fractions of the oil and with ananti-solvent which is adapted to lower the solventpower of theselective solvent for; the more parafiflnic oil fractions and which'is more soluble in the extract phase than in the' raifinate phase, removing a ramnate phase and an extract phase/from each extraction stage and progressively diminishing the quantity of antisolvent as the extraction proceeds from the initial oil feed stage to the stage-from which. the final raiiinate is withdrawn.

12. A process of refiningmineraI hydrocarbonv oils with a solvent refining agent which in' its undiluted state is relatively non-selective. as

measured by its ability to separate non-parafiinic from parafmic hydrocarbons and which when diluted with water is relatively highly selective as measured by its ability to dissolve only hydrocarbons of highly non-paraffinic character, comprising treating an oil With the solvent diluted with Water, separating the diluted solvent together with its dissolved highly non-parafiinic hydrocarbons from the remaining oil, treating the remaining oil with the undiluted solvent, and separating the undiluted solvent together with its dissolved hydrocarbons from the undissolved oil.

13. Process for separating a petroleum oil into at least three constituents of difierent characteristics which comprises treating the petroleum oil with a solvent mixture comprising an active solvent substance of the class having a solubility selectivity for aromatic type compounds and an inert solvent material of the class having substantially no solvency for petroleum oil, to obtain a raffinate and an extract of different characteristics, subjecting the raffinate in successive stages to the action of a similar solvent which in each successive stage comprises a greater proportion of the active petroleum solvent and a smaller proportion of the inert material.

14. A solvent refining process for separating a mineral hydrocarbon oil into fractions relatively more paraffinic in character and relatively less paraffinic in character, with a solvent refining agent which when employed alone is relatively non-selective as measured by its ability to separate non-paraffinic components from paraffinic components of the oil and which when diluted with an anti-solvent is relatively more selective for said non-paraninic components of the oil, comprising extracting a mineral hydrocarbon oil with said solvent refining agent diluted with an anti-solvent, separating the diluted solvent together with its dissolved components of the oil from the remaining oil, treating the remaining oil with less dilute solvent, and removing an extract phase comprising the less dilute solvent together with its dissolved hydrocarbons.

15. A process of refining mineral hydrocarbon oils with a solvent refining agent which in its undiluted state is relatively non-selective as measured by its ability to separate non-paraflinic from paraffinic hydrocarbons and which when diluted with water is relatively highly selective as measured by its ability to dissolve only hydrocarbons of highly non-paraflinic character, comprising treating an oil with the solvent diluted with water, separating the diluted solvent together with its dissolved highly non-paraffinic hydrocarbons from the remaining oil, treating the remaining oil with less dilute solvent, and removing an extract phase comprising the less dilute solvent together with its dissolved hydrocarbons.

DAVID R. MERRILL. 

